1. Field of the Invention
The present invention relates to a travel control system for an assembly carrying vehicle.
2. Description of the Related Art
An assembly carrying vehicle is used to carry the body of an automobile to be assembled in an automobile assembly line of an automobile production factory. Therefore, a system for controlling running or travel of the assembly carrying vehicles is necessary. A conventional assembly carrying vehicle is run along a predetermined energized orbit. An electrical power for the assembly carrying vehicle is supplied to the vehicle through the contact of a brush to the orbit.
The conventional assembly carrying vehicle running or travel control system will be described below. In the conventional assembly carrying vehicle running control system, the assembly carrying vehicle is generally used in a final automobile assembly line, during which parts such as seats, doors, interior, and exterior are mounted on the body after painting.
At first, a different individual work is carried out in each of a plurality of stations disposed along the orbit on which the assembly carrying vehicle runs, manually or by use of a working robot in the final automobile assembly line. The assembly carrying vehicle is moved at a slow speed in the station in which the work is manually carried out, while the assembly carrying vehicle is stopped in a perfectly positioned state in the station in which the work is carried out by use of the working robot. Generally, the manual work is carried out to mount a small part, and the work using the working robot is carried out to mount a large part such as a door. Also, in the respective stations, a height of the body carried by the assembly carrying vehicle from a floor is automatically adjusted to a height at which a worker can easily carry out the mounting work, or an appropriate height when the mounting work is carried out by use of the working robot.
The assembly carrying vehicle running control system has a control apparatus for controlling the whole system. The movement of the assembly carrying vehicle is controlled through communication between the control apparatus and the assembly carrying vehicle. The communication is carried out between a communicating unit of the assembly carrying vehicle and a plurality of access points (AP) connected to the control apparatus.
Conventionally, a fixed point communication system using optical communication has been mainly used for the communication between the assembly carrying vehicle and the access points AP. In recent years, a radio communication system has been used for the communication between the assembly carrying vehicle and the access points AP.
A technique related to such a radio go communication system is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 7-95145). In this reference, it is intended to easily check a communication status in all communication positions on a moving route of an assembly carrying vehicle. In this configuration, the assembly carrying vehicle has a communicating unit for carrying out radio communication with a communicating unit of a ground station. The assembly carrying vehicle communicating unit is provided with a controlling section and a communication position detecting section. The controlling section controls the movement of the assembly carrying vehicle, and also controls a communicating operation of the assembly carrying vehicle communicating unit. The communication position detecting section detects a communication position at which a communication with the ground station communicating unit is carried out. Then, in the conventional assembly carrying vehicle running control system, the controlling section drives the assembly carrying vehicle communicating unit in accordance with the detected result of the communication position detecting section.
When a communication test mode is instructed, the controlling unit controls the assembly carrying vehicle to carry out a test run to pass through each of a plurality of test communication positions. Also, the controlling unit controls the communicating unit to carry out a test communication with the ground station communicating unit in each of the plurality of test communication positions. Moreover, a spectrum spreading communication method may be used in the radio communication.
Next, another conventional technique with regard to the operational control of the assembly carrying vehicle will be described below. At first, a plurality of fixed indication plates are installed on a predetermined orbit on which the assembly carrying vehicle moves. The indication plates are fixedly installed on a floor. A sensor is mounted in the assembly carrying vehicle to detect the indication plate. When detecting one of the plurality of indication plates by use of the sensor, the assembly carrying vehicle acquires an operation pattern data at the detected location. The operation of the assembly carrying vehicle is defined by the operation pattern data from an external unit. The assembly carrying vehicle carries out an operation to retain or maintain a tact pitch distance, a cornering operation or a constant speed operation, until detecting a next one of the plurality of fixed indication plates by use of the sensor.
In this way, according to the conventional technique, a current position control for the assembly carrying vehicle itself is not carried out. Therefore, it is difficult to carry out a position recovery resulting from occurrence of overrun or a position displacement of the assembly carrying vehicle. Also, this requires work for changing the fixed indication plates in association with a line change. Hence, in the above configuration, the line can not be changed flexibly or easily.
Also, in the conventional assembly carrying vehicle running controller system, the control of the assembly carrying vehicle is carried out by the control apparatus through monitoring a status table of the assembly carrying vehicle.
A supersonic sensor is mounted on an assembly carrying vehicle, in order to measure a distance from a preceding assembly carrying vehicle running immediately before. The running speed of the assembly carrying vehicle can be adjusted based on the distance from the preceding assembly carrying vehicle, which is measured by the supersonic sensor. Thus, the assembly carrying vehicle can be moved while keeping a constant interval from the preceding assembly carrying vehicle. When the assembly carrying vehicle is running on a corner on a predetermined orbit, the supersonic sensor may likely sense things other than the preceding assembly carrying vehicle. For this reason, it is impossible to accurately measure the distance from the preceding assembly carrying vehicle on the corner. Hence, when the assembly carrying vehicle is running on the corner, the running control can not be carried out by use of the supersonic sensor. Especially, if the assembly carrying vehicle is urgently stopped on the corner, a succeeding assembly carrying vehicle may collide with the preceding assembly carrying vehicle.
Also, in the conventional assembly carrying vehicle running control system, the running or travel control of the assembly carrying vehicle is carried out through optical communication between the control apparatus and the communicating unit of the assembly carrying vehicle via a relaying unit, which is provided for one of the plurality of fixed indication plates. The assembly carrying vehicle receives control data such as a running operation and the height of a carried member through the communication. Then, the assembly carrying vehicle is moved to the next fixed indication plate based on the control data. For this reason, when trouble occurs in a part of the fixed indication plates, the assembly carrying vehicle can not be correctly controlled.
In conjunction with the above description, a spectrum spreading communication apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 5-75573). In this reference, a received signal is subjected to FFT frequency analysis to extract noise. The extracted noise is subjected to inverse FFT transformation. The noise is inverted and added to the received signal. As a result, the noise is removed from the received or cancelled signal.
Also, a train position detecting apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 5-24538). In this reference, a spread signal is alternately sent to crossed induction lines from a pair of antennas which are provided on a train. A receiver is provided to carry out an inverse spreading operation. In this way, it can be detected that the pair of antennas of the train is positioned on one of the loops.
Also, a train detecting apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 7-81567). In this reference, a PN code sequence of PN1 code and a PN2 code is spread and modulated to produce a modulation signal. The modulation signal is transmitted from a ground transmitting side to a loop P. A signal is received and demodulated by a ground receiving side, and the PN code sequence is extracted from the demodulated signal by use of a low pass filter. Then, each of the PN codes is detected by use of correlation matched filters. From a train, a signal which has been spread and modulated with the PN1 code is always transmitted from the head portion of the train to the loop. Also, a signal which has been spread and modulated with the PN2 code is always transmitted from the last portion of the train to the loop. In this way, when only the PN code contained in the signal from the ground transmitting side is detected, a relay CHR is turned on. Thus, it is detected that there is no train. When the PN code contained in the signal from the ground transmitting side and the PN1 code from the head portion of the train are detected, the relay CHR is turned off and a relay INR is turned on. Thus, it is detected that the train is coming in the loop. When the PN code contained in the signal from the ground transmitting side and the PN2 code from the last portion of the train are detected, the relay CHR and the relay INR are turned off and a relay OUTR is turned on. Thus, it is detected that the train is going out from the loop.
Also, a moving vehicle control facility is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 7-182038). In this reference, memory media are provided along a running route L of a moving vehicle. Each of the memory media is composed of a storage section for storing control data of the moving vehicle, and a communicating section for communicating the control data. The moving vehicle is composed of a read section for reading the control data through communication with one of the memory media and a control unit,for controlling the operation of the moving vehicle based on the control data. In such a system, the control data is divisionally stored in a plurality of memory media TPA and TPB which are arranged adjacent to each other along the running route L. The control section reads out the control data from the memory media TPA and TPB while the moving vehicle runs on the running route L.
Therefore, an object of the present invention is to provide an assembly carrying vehicle travel control system in which a current position of an assembly carrying vehicle can be accurately detected.
Another object of the present invention is to provide an assembly carrying vehicle travel control system in which an assembly carrying vehicle can be always controlled by a control apparatus.
Still another object of the present invention is to provide an assembly carrying vehicle travel control system in which the running state of an assembly carrying vehicle on a corner of an orbit can be properly managed by a control apparatus.
Yet still another object of the present invention is to provide an assembly carrying vehicle travel control system in which a collision between assembly carrying vehicles on a corner can avoided.
It is also an object of the present invention to provide an assembly carrying vehicle travel control system in which stoppage of the running operation of the assembly carrying vehicle is assured even when one of a plurality of access points has failed.
Another object of the present invention is to provide an assembly carrying vehicle travel control system in which a control apparatus can communicate with an assembly carrying vehicle irrespective of the position of the assembly carrying vehicle.
Still another object of the present invention is to provide an assembly carrying vehicle travel control system in which a control apparatus can always communicate with an assembly carrying vehicle via access points.
Yet still another object of the present invention is to provide an assembly carrying vehicle travel control system in which a high speed roaming operation by an assembly carrying vehicle can be made possible when the control apparatus communicates with the running assembly carrying vehicle through one of a plurality of access points.
It is an object of the present invention to provide an assembly carrying vehicle travel control system in which collisions between assembly carrying vehicles can be avoided, even when any failure occurs in the running assembly carrying vehicles.
In order to achieve an aspect of the present invention, an assembly carrying vehicle travel control system includes a plurality of assembly carrying vehicles, a control apparatus, and a plurality of access points. The plurality of access points are connected with the control apparatus and provided for the plurality of assembly carrying vehicles. Each of the plurality of access points has a communication area. When each of the plurality of assembly carrying vehicles is individually in the communication area of a currently communicating one of the access points, the assembly carrying vehicle transmits an operation status data indicative of an operation status thereof to the control apparatus through the currently communicating access point. The control apparatus determines an operation control instruction based on the operation status data to transmits the instruction to the assembly carrying vehicle. The assembly carrying vehicle receives the operation control instruction from the control apparatus through the currently communicating access point such that an operation of the assembly carrying vehicle is controlled based on the operation control instruction.
In this case, the control apparatus may issue a state notice request signal to the plurality of access points. Each of the plurality of access points transmits an access point operating state data indicating an operating state thereof to the control apparatus. The control apparatus determines a failed one of the plurality of access points based on the access point operating state data.
Also, it is desirable that each of the plurality of access points has a peculiar data and transmits the peculiar data to the control apparatus in response to the state notice request signal from the control apparatus when the access point has not failed. The control apparatus determines the failed access point from the transmitted peculiar data from the plurality of access points. Alternately, each of the plurality of access points may transmit the peculiar data to the control apparatus in response to the state notice request signal from the control apparatus when the access point has failed. At that time, the control apparatus determines the failed access point from the peculiar data transmitted from the plurality of access points.
Also, the control apparatus and the plurality of access points may be connected with a LAN using Ethernet.
The plurality of access points are arranged such that electric field intensity levels of reception signals from a predetermined number of ones of the plurality of access points are equal to or higher than a first threshold intensity level. In this case, the plurality of access points are desirably arranged such that the electric field intensity level of the reception signal from at least one of the predetermined number of access points is equal to or higher than a second threshold intensity level. Here, the second threshold intensity level is higher than the first threshold intensity level. Also, the predetermined number may be at least 2.
Also, the plurality of access points may be arranged such that electric field intensity levels of reception signals from two or more of the plurality of access points are at least a predetermined threshold intensity level.
Also, the currently communicating access point may include a communicating unit to communicate with the assembly carrying vehicle. In this case, the control apparatus transmits the operation control instruction to the assembly carrying vehicle via the currently communicating access point. Each of the assembly carrying vehicle may include a communicating unit communicating with the currently communicating access point and with the control apparatus via the currently communicating access point, and a control unit controlling the operation of the assembly carrying vehicle based on the operation control instruction received from the control apparatus via the currently communicating access point. In this case, it is desirable that the communication between the currently communicating access point and the one assembly carrying vehicle is a spectrum spreading communication of a frequency hopping system.
Also, the control apparatus may determine the operation status of the assembly carrying vehicle based on the operation status data transmitted from the assembly carrying vehicle, and transmit an operation status data indicative of the determined operation as the operation control instruction to the assembly carrying vehicle. Also, the assembly carrying vehicle may further include a high speed roaming table, which stores next communicatable ones of the plurality of access points. The next communicatable access points are associated with the currently communicating access point. In this case, the control unit selects one of the next communicatable access points stored in the high speed roaming table as a new currently communicating access point when an electric field intensity of a reception signal from the currently communicating access point becomes lower than a predetermined threshold intensity level. Each of the plurality of access points may also have a high speed roaming table to store the next communicatable access points. The communicating unit of the assembly carrying vehicle receives the next communicatable access points from the currently communicating access point. The control unit stores the next communicatable access points received from the currently communicating access point in the high speed roaming table of the assembly carrying vehicle.
Also, the control unit selects one, having a maximum reception signal electric field intensity level, of the next communicatable access points stored in the high speed roaming table of the assembly carrying vehicle, when the reception signal electric field intensity level from the currently communicating access point is lower than the predetermined threshold intensity level.
Also, the control apparatus may include an input unit used to input the next communicatable access points for each of the plurality of access points, and a which notifies unit notifying the inputted next communicatable access points to the plurality of access points, respectively. Each of the plurality of access points stores the next communicatable access points received from the control apparatus in the roaming table thereof.
Also, each of the plurality of assembly carrying vehicles has a status table indicating the operation status of the assembly carrying vehicle. The communicating unit of the assembly carrying vehicle transmits a data of the status table as the operation status data to the control apparatus through the currently communicating access point. In this case, the data of the status table may include: a current position data indicative of a current position of the assembly carrying vehicle; the operation status data indicative of the operation status of the assembly carrying vehicle; and a failure indication data indicative of a failure in the assembly carrying vehicle. The communicating unit notifies the operation status data of the assembly carrying vehicle to the control apparatus, when the operating status data or the failure indication data of the assembly carrying vehicle is updated. In this case, the control apparatus may further include a display unit displaying at least one of the current position of the assembly carrying vehicle, the operation status thereof, and existence or non-existence of the failure based on the operation status data transmitted from the assembly carrying vehicle.
Also, the assembly carrying vehicle travel control system may further include a plurality of position indication members provided along an orbit, the assembly carrying vehicle traveling on the orbit. It is desirable that each of the assembly carrying vehicles includes a position indication member detector which detects each of the plurality of indication members, and a running distance measuring unit measuring a running distance of the assembly carrying vehicle from a start point of the orbit to a current position of the assembly carrying vehicle, or from one of the plurality of position indication members to a next one of the plurality of position indication members. In this case, the communicating unit of the assembly carrying vehicle transmits a failure indication data to the control apparatus when a difference between a position corresponding to one of the position indication members detected by the position indication member detector and a position corresponding to the running distance measured by the running distance measuring unit is larger than a predetermined value. Also, the running distance measuring unit measures the running distance of the assembly carrying vehicle based on a number of rotations of a motor to drive a wheel of the assembly carrying vehicle.
Also, each of the assembly carrying vehicles may further include an operation table, which stores a plurality of operation data indicative of operations to be executed by the assembly carrying vehicle. The control unit acquires a specific one of the plurality of operation data from the operation table and carries out the operation corresponding to the acquired operation data. In this case, the communicating unit receives a plurality of operation data from the control apparatus at a start point of the orbit, and the control unit stores the plurality of operation data received by the communicating unit in the operation table. Also, the plurality of operation data may be stored by the control unit in the operation table in an order of execution. In this case, the control units accesses to the operation table based on a number of position indication members detected by the position indication member detector from the start point of the orbit to acquire one of the plurality of operation data, and executes the operation corresponding to the acquired operation data. Alternatively, when the plurality of operation data are stored in the operation table based on the distance from the start point of the orbit and, the control units accesses to the operation table based on the running distance measured by the running distance measuring unit to acquire one of the plurality of operation data, and executes the operation corresponding to the acquired operation data.
Also, when each of the plurality of operation data received by the communicating unit contains a distance data, the control unit may search the operation table for one of the plurality of operation data having a distance data corresponding to the running distance measured by the running distance measuring unit, and carry out any such operation data found by the search. In this case, the control unit may continue to carry out a current one of the operation data, when any of the operation data having the distance data corresponding to the running distance measured is not found by the search.
Also, the control unit may transmit the operation status data indicative of failure occurrence to the control apparatus when the position indication member detector does not detect any position indication member for a predetermined time interval after a previous position indication member is detected. Then the control apparatus transmits a stop request signal as the operation control instruction to the plurality of assembly carrying vehicles, and the control unit of the assembly carrying vehicle stops the running of the assembly carrying vehicle in response to the stop request signal. In this case the control system is a operative according to the equations:
I less than T1xc3x97V
T1 less than W/Vxe2x88x92T2
where I is a distance between the previous position indication member and the position indication member currently detected, T1 is the predetermined time interval, V is a velocity of the assembly carrying vehicle, W is a distance between the assembly carrying vehicle and a preceding one of the plurality of assembly carrying vehicles, and T2 is a time interval from transmission of the operation status data indicative of failure occurrence by the preceding assembly carrying vehicle to reception of the stop request signal.
Also, the current position of the assembly carrying vehicle is updated based on a position data corresponding to the position indication member currently detected by the position indication member detector.
In another aspect, a control method of an assembly carrying vehicle in an assembly carrying vehicle travel control system, is attained by the steps of arranging a plurality of position indication members along an orbit, each of a plurality of assembly carrying vehicles running on the orbit; providing a plurality of access points connected to a control apparatus, each of the plurality of access points has a communication area, and each of the assembly carrying vehicles being communicatable with one of the plurality of access points as a currently communicating access point when the assembly carrying vehicle is in the communication area of the one access point; transmitting from the assembly carrying vehicle an operation status data indicative of an operation status thereof to the control apparatus through the currently communicating access point; determining by the control apparatus an operation control instruction based on the operation status data and transmitting the operation control instruction to the assembly carrying vehicle; receiving the operation control instruction by the assembly carrying vehicle from the control apparatus through the currently communicating access point; and controlling operation of the assembly carrying vehicle based on the operation control instruction received from the control apparatus via the currently communicating access point.
The control method may further include the steps of: detecting each of the plurality of position indication members; measuring a running distance of the assembly carrying vehicle from a start point of the orbit to a current position of the assembly carrying vehicle, or from one of the plurality of indication members to a next one of the plurality of indication members; determining a current position of the assembly carrying vehicle based on at least one of the detected position indication members or the measured running distance: receiving and storing a plurality of operation data indicative of operations to be executed by the assembly carrying vehicle in an operation table; controlling the operation of the assembly carrying vehicle based on a specific one of the plurality of operation data which is determined based on the determined current position; updating a status table indicating the operation status of the assembly carrying vehicle based on at least one of change of the operation status of the assembly carrying vehicle, change of the at least one detected position indication member or the measured running distance, and a failure of the assembly carrying vehicle; and transmitting the status table as the operation status data from the assembly carrying vehicle to the control apparatus.
The step of providing a plurality of access points is attained by transmitting a state notice request signal from the control apparatus to the plurality of access points; transmitting from each of the plurality of access points an access point operating state data indicating an operating state thereof to the control apparatus; and determining a failed one of the plurality of access points by the control apparatus based on the access point operating state data.
Also, when each of the plurality of access points has a peculiar data, the control method may further include the step of: notifying the peculiar data from each of the plurality of access points to the control apparatus in response to the state notice request signal from the control apparatus, when the access point has not failed; and the step of determining a failed one of access points involves determining the failed access point from the notified peculiar data from the plurality of access points. Alternately, when each of the plurality of access points has a peculiar data, the control method may further include the step of: notifying the peculiar data from each of the plurality of access points to the control apparatus in response to the state notice request signal from the control apparatus, when the access point has failed; and the step of determining a failed one of access points involves determining the failed access point from the notified peculiar data from the plurality of access points.
Also, the control apparatus and the plurality of access points may be connected with a LAN using Ethernet.
Also, the step of providing a plurality of access points may be attained by arranging the plurality of access points such that electric field intensity levels of reception signals from a predetermined number of ones of the plurality of access points are higher than a first threshold intensity level. In this case, the step of providing a plurality of access points may include: arranging the plurality of access points such that the electric field intensity level of the reception signal from at least one of the predetermined number of access points is higher than a second threshold intensity level, the second threshold intensity level is higher than the first threshold intensity level. It is desirable that the predetermined number is equal to or more than 2.
Also, the step of providing a plurality of access points may be attained by arranging the plurality of access points such that electric field intensity levels of reception signals from two or more of the plurality of access points are higher than a predetermined threshold intensity level.
Also, communication between the currently communicating access point and the assembly carrying vehicle may be a spectrum spreading communication of a frequency hopping system.
Also, the step of determining an operation control instruction may include: determining the operation status of the assembly carrying vehicle by the control apparatus based on the operation status data transmitted from the assembly carrying vehicle, and transmitting an operation data indicative of the determined operation status as the operation control instruction to the assembly carrying vehicle.
The control method may further include the step of: selecting one of next communicatable access points stored in a high speed roaming table of the assembly carrying vehicle as a new currently communicating access point, when an electric field intensity of a reception signal from the currently communicating access point becomes lower than a predetermined threshold intensity level, wherein the next communicatable access points are associated with the currently communicating access point. In this case, when each of the plurality of access points also include a high speed roaming table to store the next communicatable access points, the step of selecting one of next communicatable access points may be attained by receiving the next communicatable access points from the currently communicating access point to store in the high speed roaming table of the assembly carrying vehicle.
Also, the selecting step may include: selecting one, having a maximum reception signal electric field intensity level, of the next communicatable access points stored in the high speed roaming table of the assembly carrying vehicle, when the reception signal electric field intensity level from the currently communicating access point is lower than a predetermined threshold intensity level.
Also, the selecting step may be attained by inputting the next communicatable access points for each of the plurality of access points in the control apparatus; by transmitting the inputted next communicatable access points to the plurality of access points, respectively; and by storing the next communicatable access points received from the control apparatus in the roaming table of each of the plurality of access points.
Also, the control method may further includes the step of: Also, displaying at least one of the current position of the assembly carrying vehicle, the operation status thereof, and existence or non-existence of the failure of the assembly carrying vehicle based on the operation status data notified from the assembly carrying vehicle.
The control method may further include the step of: transmitting a failure indication data from the assembly carrying vehicle to the control apparatus when a difference between a position corresponding to a detected one of the position indication members and a position corresponding to the measured running distance of the assembly carrying vehicle is larger than a predetermined value.
Also, the measuring step includes: measuring the running distance of the assembly carrying vehicle based on a number of rotations of a motor driving a wheel of the assembly carrying vehicle.
The step of receiving and storing a plurality of operation data may include: receiving the plurality of operation data from the control apparatus at a start point of the orbit; and storing the plurality of received operation data in the operation table. In this case, the step of storing the plurality of received operation data may be attained by storing the plurality of received operation data in the operation table in an order of execution, and the step of controlling operation of the assembly carrying vehicle may be attained by accessing the operation table based on a number of position indication members detected from the start point of the orbit to acquire one of the plurality of operation data; and carrying out the operation corresponding to the acquired one of the plurality of operation data.
Also, the storing the step of plurality of received operation data may be attained by storing the plurality of received operation data in the operation table based on the running distance from the start point of the orbit, and the step of controlling an operation of the assembly carrying vehicle may be attained by accessing the operation table based on the measured running distance to acquire one of the plurality of operation data; and carrying out the operation corresponding to the acquired one of the plurality of operation data.
Also, when each of the plurality of operation data contains a distance data, the step of controlling an operation of the assembly carrying vehicle may be attained by searching the operation table for a specific one of the plurality of operation data having a distance data corresponding to the measured running distance and carrying out any such operation data found by the search. In this case, the step of controlling an operation of the assembly carrying may include: continuing to carry vehicle out a current operation data when any operation data having the distance data corresponding to the measured distance measured is not found by the search.
Also, the step of controlling an operation of the assembly carrying vehicle may include: transmitting the operation status data indicative of failure occurrence to the control apparatus when any of the position indication members is not detected for a predetermined time interval after a previous position indication member is detected. The control method may further include the step of: transmitting by the control apparatus a stop request signal as the operation control instruction to the assembly carrying vehicle upon receiving the operation status data indicative. Also, the step of controlling an operation of the assembly carrying vehicle may stop the running of the assembly carrying vehicle in response to the stop request signal. In this case the method is operative according to the equations,
I less than T1xc3x97V
T1 less than W/Vxe2x88x92T2
where I is a distance between the previous position indication member and the position indication member currently detected, T1 is the predetermined time interval, V is a velocity of the assembly carrying vehicle, W is a distance between the assembly carrying vehicle and a preceding one of the plurality of assembly carrying vehicles, and T2 is a time interval from transmission of the operation status data indicative of failure occurrence by the preceding assembly carrying vehicle to reception of the stop request signal.
Also, the current position of the assembly carrying vehicle is updated based on a position data corresponding to the detected position indication members.